Theoretical strength of 2D hexagonal crystals: application to bubble raft indentation

By means of lattice and molecular dynamics we study the theoretical strength of homogeneously strained, defect-free 2D crystals whose atoms interact via pair potentials with short- and longer-ranged interactions, respectively. We calculate the instability surface, i.e. the boundary in the 3D homogeneous strain space (ε _xx ,?ε _yy ,?ε _xy ), at which the first vanishing of the frequency of a vibrational mode occurs, taking into account all 2(N???1)?+?3 modes of a 2D periodic system of N atoms. We also compute the strain energies of the crystal on the instability surface, thus defining the most dangerous direction(s) of strain where the critical energy density is small. A theory is developed to incorporate the effect of loading device–sample interactions in the lattice instability criterion. The results are applied to the model problem of bubble raft indentation. We analyse the distribution of the unstable phonon modes in the first Brillouin zone as a function of the loading parameter, and discuss the post-critical behaviour of the lattice in the presence of strain gradients as in nano-indentation experiments.     

Generalized Feistel networks revisited

This work deals with the classification, security and efficiency of generalized Feistel networks (GFNs) with 4 lines. We propose a definition of a GFN, essentially limiting consideration to Feistel-type constructions with domain-preserving F-functions and rotation by one line between rounds. Under this definition, we demonstrate that there are only two non-contracting representatives in the class of 4-line GFNs up to equivalence, namely, the type-I and type-II GFNs that avoid obvious differential effects. We propose to instantiate the GFNs with SPS-functions (two substitution layers separated by a permutation layer) instead of single SP-functions (one substitution-permutation layer only). We prove tight lower bounds on the number of differentially and linearly active functions and S-boxes in such ciphers. We show that the instantiation with SPS-functions using MDS diffusion provides a proportion of differentially and linearly active S-boxes by up to 33 and 50 % higher than that with single SP-functions for type-I and type-II GFNs, respectively, if the same matrix is used in all rounds. Moreover, we present the upper bounds on the differential and the linear hull probability for the type-II GFNs with SPS-functions. This opens up the possibility of designing more efficient block ciphers based on GFN structure.     

Planar mobility modes of 8-bar-jointed structures with a single degree of freedom

A range of modes of mobility for spatial structures can be achieved by selecting the rotational features of the joints. Similar mechanical characteristics are observed in structures ranging from molecules to buildings. The local rotational manner in a solid with an internal spatial structure performs a key part in dictating the nature of structural deformability. In this paper, we propose a two-dimensional repetitive motion structure assembled with straight rigid bars connected by 8-bar pivot joints. By determining the rotational modes of the 8-bar joint with certain geometrical constraints, we introduce some telescopic transformations of the proposed structure producing both well-known and novel motions. In addition, we verify one of the deployable mechanisms by manufacturing it and testing activation by a single rotary operation.     

On-chip micellar electrokinetic chromatographic separation of phenolic chemicals in waters

This paper describes on-chip micellar electrokinetic chromatography (MEKC) separation of bisphenol A and 3 kinds of alkylphenols, which have been recently recognized as endocrine disrupting chemicals for fish by the Japanese government, using microchip capillary electrophoresis with UV detection. We successfully obtained high-speed separation of the phenolic chemicals within 15 s as optimizing in microfluidic controls and MEKC separation conditions. We obtained fairly good linearity with correlation coefficient of over 0.98 from 0 to 50 mg/l phenolic chemicals except for 4-nonylphenol, which sample is the mixture of many geometrical isomers (r = 0.86). The values of the relative standard deviation for peak height in 50 mg/l phenolic chemicals were less than 8% except for bisphenol A (11.0%). The limits of detection obtained at a signal-to-noise ratio of 3 were from 5.6 to 20.0 mg/l. To realize on-site monitoring, we described strategy for on-chip MEKC analysis of the phenolic chemicals in waters using a portable analyzer based on microfluidic devices.     

Multiple shear banding in a computational amorphous alloy model

The strain localized phenomenon, so called shear bands (SBs), in an amorphous alloy have received a lot of attention in recent years. In this study, we microscopically investigated the nature and dynamics of multiple SBs using molecular dynamics model. In the SB region, intense shear-induced structural change occurred, typified by the annihilation of pentagonal short-range order, and significant localized heating accompanied with the SB propagation was observed. Moreover, a large number of fine SBs operated simultaneously at a high strain rate, whereas, only a few SBs appeared and propagated abruptly at a low strain rate. These results were discussed with respect to brittle/ductile deformation of bulk metallic glasses. PACS 31.15.xv; 62.20.F-; 81.05.Kf     

Serially grafted polymer optical waveguides fabricated by light-induced self-written waveguide technique

Serially grafted polymer optical waveguides were fabricated by the light-induced self-written (LISW) waveguide technique for the first time to our knowledge. To realize functional waveguide cores by the LISW technique, transparent materials at the writing wavelength were selected. By inserting thin transparent partitions, a serial-graft structure consisting of passive and active waveguides without any misalignment was realized automatically. This technique is advantageous for its extremely easy process over conventional fabrication techniques.     

Synthesis and photochromism of spirobenzopyran derivatives bearing an oxymethylcrown ether moiety: metal ion-induced switching between positive and negative photochromisms

Spirobenzopyran derivatives carrying an oxymethylcrown ether moiety were synthesized, and their photochromism was studied in the presence of various metal ions in acetonitrile. The metal ion complexing ability of the crown ether moiety in crowned spirobenzopyrans affects both thermal isomerization and photoisomerization of their spirobenzopyran moiety to a great extent. When the interaction of the crown ether moiety with a metal ion was strong enough to cause thermal isomerization of the spirobenzopyran moiety to its corresponding merocyanine form and to suppress UV-induced isomerization to the merocyanine form, a negative photochromism appears. On the other hand, a relatively weak interaction of the crown ether moiety with a metal ion affords a positive photochromism. This phenomenon enables us to switch the photochromic behavior between positive and negative photochromisms.     

Naphthoquinonedioxime derivatives as analytical reagents for the spectrophotometric determination of nickel

Seven naphthoquinonedioxime compounds, including five new compounds. were synthesized and their reactions with nickel, cobalt and iron(II) ions were examined. The metal chelates of these dioximes absorb in the visible region, and the molar absorptivities of the complexes are about 1 · 10⁴ 1 mole^-1 cm^-1 in

aqueous solution. The chelates can be extracted into chloroloform with zephiramine. and the molar absorptivities of the nickel chelates are about 2 · 10⁴ 1 mole^-1 cm^-1. Of the dioximes examined. 1,2-naphthoquinonedioxime-6-sulfonic acid shows the highest sensitivity for nickel; the molar absorptivity of the nickel complex extracted into chloroform with zephiramine is 2.19 · 10⁴ I mole^-1 cm^-1 at 468 nm.     

A new cyclopentanone annulation of α-bromomethylacrylates

Direct couplings of the α-bromomethylacrylates and the doubly charged succinate ion are described.     

Mesomorphic phase formation of poly (macromonomer)s of polystyrene macromonomers

The liquid crystalline phase formation of poly(macromonomer)s associated with the specific multibranched architecture of high branch density was investigated. The poly(macromonomer)s were prepared by radical chain polymerizations of ω‐methacryloyloxyethyl polystyrene macromonomers. It was confirmed that the mesomorphic phase formation depended on the branching architecture, where sufficient length of the branch chains as well as the backbone chain is crucial for the formation of the mesomorphic phase. Formation of the optically anisotropic mesophase also depended on the nature of solvent. The mesophase was observed in the cast films prepared from p‐xylene, toluene, tetrahydrofuran, carbon disulfide and chloroform but not observed for cyclohexane. The effects of the branched structure and the solvent nature were explained by repulsive interaction between the polystyrene branch chains of high branch density. The repulsive interaction increases the chain stiffness of the central backbone and also prevents the interpenetration of the polystyrene branches of different molecules in solution, which allow poly(macromonomer) molecules to arrange with the orientational order. Copyright © 2000 John Wiley & Sons, Ltd.